Various methods for preparing solid semi-solid polymers from hydrocarbons, e.g. from 1-olefines have been developed.
In one such method olefines, such as ethylene, propene, butene or pentanes, are polymerized in the presence of catalysts in hydrocarbon diluents or the monomers themselves act as diluents. Reactants are then kept in a solution phase by maintaining a suitable pressure in the polymerization reactor. When the resultant polymer is insoluble or slightly soluble in said diluent, the polymer product is formed as particles and the product flow thus comprises a suspension formed by polymer particles, a diluent and monomers. This product flow is usually led into a polymer separation container, in which the solid substances as well as liquid and gaseous constituents are separated from each other.
One reactor type applied in such methods is a continuous tube reactor forming a loop, in which reactor the polymerization occurs in a turbulent flow circulating in a loop. The product containing the polymer, a diluent and monomer is taken from the loop reactor either continuously or more usually discontinuously via a discharge valve, and it is led to a separator, in which the polymer is separated by reducing the pressure.
For regulating the polymerization reaction, it is possible to take samples continuously or discontinuously from the product flow of the reactor. The normal way of taking a sample from the gas flow exiting from the polymer separation container and of analyzing this sample with various methods, e.g. by means of gas chromatography. Such an arrangement is described e.g. in U.S. Pat. No. 3,556,730.
In this known procedure the delay which is needed from the exiting of the product from the polymerization reactor to the initial moment of the analysis, is often considerably long and essential changes can occur meanwhile in the process. In other words, the sampling according to this patent is coupled directly to the reactor, so the sample represents the condition which prevailed in the reactor at the moment of taking the sample. The sample is thus not in all times representative. It would then be preferable that the analysis delay could be shortened.